An existing NTSC television receiver is controlled by a microcomputer which communicates with various receiver subsystems via a data bus. The receiver design may include a multi function integrated circuit which provides most of the sub-subsystems required in an NTSC TV receiver. To facilitate the display signals other than those conforming to the NTSC synchronizing standard may involve the use of a multi-standard sync generator. The multi-standard sync generator may be interfaced to the existing IC sub-subsystems for signal extraction, and signal reinsertion. However, cost and device availability may preclude the use of additional bus controllable multi-standard integrated circuits. Furthermore, to minimize additional manufacturing costs resulting from such a multi-standard requirement, the design should utilize the same test fixtures and retain the same automated, computer controlled set up and alignment capability employed for the basic single standard chassis.
An existing multifunction integrated circuit sync generator is designed for NTSC synchronizing standard operation and as such, without an input sync signal, the sync generator defaults to nominal NTSC sync parameters. Under the same no signal conditions a multi-standard sync generator defaults to nominal sync parameters of, for example, a 625 line 50 Hz standard. The cost/design constrains result in an inevitable interconnection between the two sync generation systems which coexist satisfactorily when externally synchronized. However, with no input sync signal, the two sync generator default standards are substantially different, resulting in spurious signal generation and difficulty in determining and setting the free running frequency of the NTSC only generator.